1. Field of the Invention
This invention relates to a method of producing colored images on various substrates. By first coating the substrate with a sealer and when dried, coating with a water based pigmented photo-sensitive coating; after drying, exposing this coating to ultraviolet light through a photographic negative, and developing this image by removing the unexposed portion with water. These colored images using this process are particularly useful in preparing direct images, transfer or rub off images, and can also be used in preparing pre-press proofs that more closely resemble actual press proofs or press runs than similar proofs from the techniques of the prior art.
2. Description of the Prior Art
The color printing industry is, of course, massively large, with billions of dollars going toward the creation of beautiful color reproductions of photographs for magazines, art work, sales brochures, and the like.
As a color print job is laid out, it is often necessary to prepare a color proof or composition for careful examination prior to going forward with the substantial expense of setting up the press for commercial printing of the color reproduction. The original art work might consist of a single negative or multi negatives for complex color work, or it might consist of accurate four color separations to reproduce process color images.
A disadvantage of the prior art process is that most direct imaging and transfer systems use solvent based ink solutions which contain flammable or hazardous materials. In addition, a clear solvent solution or solutions which are also flammable or hazardous must be used for these images to be developed after exposure to ultraviolet light.
When using the method which uses a solvent based ink, another disadvantage is that the system will not hold fine line detail which is necessary in many cases of reproductions of art work and mandatory when required to make a detailed four color process image.
In Lupo, U.S. Pat. No. 2,716,061, a pigmented contact printing emulsion is disclosed for use in reproducing multi-colored photographic images on flexible supports, and especially vinyl plastic sheets. While having some similarity to the invention of this application, the formulations disclosed in the Lupo patent exhibit significant disadvantages, and are not practically capable for commercial use in the preparation of direct imaging, transfer lettering or, pre-press proofs.
Substantial disadvantages are found in the commercially available formulation of the Lupo patent compared with the preferred formulations of this invention. First, the formulation of the Lupo patent is less viscous and when a substrate is coated by placing it in a conventional whirler it dries unevenly and leaves mottled areas having different color densities. Furthermore, the exposed coating of the prior art patent tends to wash away more easily than the exposed coating in accordance with this invention after a comparable amount of exposure to ultraviolet light.
The photosensitive emulsion or varnish of this invention requires less ultraviolet light exposure time to cure. Furthermore, the exposed photosensitive coating of this invention may be washed with pure water to remove the noncross-linked portions, rather than requiring an ammonium hydroxide solution for washing as in the prior art.
The prior art formulations are applied, in their commercially available forms, by hand application to a backing by the whirler process. It is then dried by conventional methods after which a photographic negative is laid over the coating which is on a substrate and is exposed to ultraviolet light. After the desired exposure period, the negative is then removed and the portions of the coating underneath the transparent parts of the negative are rendered insoluble. When the negative is removed, the substrate with a particular color which has just been exposed is washed with a dilute ammonia solution to remove the portions of the applied coating which were not rendered insoluble by exposure to ultraviolet light.
Prior art processes used commercially in producing pre-press proofs consist of expensive mechanical equipment and involve the use of micropulverized pigmented material which is applied to a sensitized flexible film by hand or some mechanical means. Then the proper negative is placed over the flexible film which has the color applied and is exposed to ultraviolet light. After exposure the negative is removed and the applied color on the sensitized flexible film is developed. Successive sensitized films are used, each having its specific color. When the required number of flexible films are developed they are laminated after they are placed in register, however, the laminations cause a gloss and depth of image which is not achieved when the job is actually printed.